Retaining walls are used in various landscaping projects and are available in a wide variety of styles. Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured concrete, precast panels, masonry, and landscape timbers or railroad ties.
A widely accepted method of construction of such walls is to dry stack concrete wall units, or blocks. These blocks are popular because they are mass produced and, consequently, relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install. Because they comprise concrete, they are durable. They can be given a desired appearance, such as, for example, natural stone. Many block systems also use pins that are adapted to fit in corresponding pin holes in adjacent blocks or may use other mechanical means to contribute to the stability of a wall.
Typically, retaining wall blocks are manufactured to have the desired appearance on the front face (i.e., the outer face of a wall) because only the front is visible after the wall is constructed. It is highly desirable to have the front face of the wall system have a natural stone appearance, and many approaches are used in the art to treat or process concrete to evoke the appearance of natural stone, including splitting the block, tumbling the block to weather the face and edges of the face, and using processing or texturing equipment to impart a weathered look to the concrete.
Depending upon their location, the soil type, the amount of water that can flow through the wall, and the mineral content of the water, an undesirable appearance can develop on the surface of a retaining wall. In addition, due to exposure to the elements and freeze/thaw cycles, concrete retaining walls may exhibit spalling, that is, chipping and cracking of concrete, which affects their appearance and can ultimately affect their utility. Freeze-thaw effects are worsened when the wall face is exposed to salt spray, which commonly occurs on roadways where de-icing salts are used to clear the road of ice and snow. Efflorescence refers to the leaching of mineral salts from water and this often occurs on walls in contact with water. The resultant deposit on a surface creates an unattractive white stained appearance on a wall.
There have been prior efforts to add a veneer to regular and segmental retaining walls with natural stone or concrete that is pre-cast molded to closely resemble natural stone. While such veneering produces aesthetically pleasing walls, it is a laborious and highly expensive process, as it requires skilled masonry work to tie in the stone or concrete veneer to the wall using traditional mortared masonry construction methods. Such veneering can double the cost of the finished wall. In addition, segmental retaining walls are not rigid structures and applying a rigid mortared veneer may cause cracking unless appropriate steps are taken to provide slip joints that allow for such movement. Veneers for retaining walls are described in US 2005/0252144 A1, the contents of which are incorporated by reference herein.